The electro-magnetic environment surrounding us, and in particular, surrounding a radar installation may be thought of as a continuum in which events acting on the continuum are not localized or found in isolation but, rather, are felt, and act on, the entire continuum, subject to naturally occurring attenuation. Further, it is not only events which cause what are described as ripples or waves which affect the continuum, but also the converse of such events, wherein a hole or void also affects the continuum. It is with respect to the latter that the present specification is directed.
As well documented in the prior art, such as described by Brinsfield in U.S. Pat. No. 5,808,577 which issued Sep. 15, 1998 for a Stealth Aircraft Identification System, stealth aircraft, that is, which are normally not detected by airborne, ground or sea based radar systems, have external contours that redirect return signals in non-threat directions so that little of the incident radar signal is detected, and which aircraft are partially or completely coated with radar absorbing materials that are fabricated using internal structures that also absorb the incident radar signal. Typical radar absorbent material include iron particles dispersed in a resin matrix material, either as a paint or structural material such as composite skin.
Messano in his U.S. Pat. No. 7,212,147 which issued May 1, 2007 for a Method of Agile Reduction of Radar Cross Section using Electromagnetic Channelization describes that stealth technologies rely on five elements to minimize the size of the radar cross section of a target: namely, radar absorbent material, internal radar absorbent construction, external low absorbable geometry, infrared emissions control, and specialized mission profiles. Messano describes the radar absorbent material approach incorporates the use of coatings containing iron ferrite material which transform the electric component of the incoming radar wave into a magnetic field so that consequently the energy of the incoming radar wave is allowed to dissipate.
Applicant is also aware of published U.S. Patent Application, Publication No. 2012/0268305, in the application of Macsisak, published. Oct. 25, 2012 and entiltled Stealth. Detector. Macsisak describes a stealth detector having three radars which are aimed at slightly different angles so that the corresponding three radar signals will each send a radar signal back to a radar installation where a computer or analyst determines if the three radar signals show the detected object to be a stealth plane.
Geer in his U.S. Pat. No. 7,952,511 which issued May 31, 2011 for a Method and Apparatus for the Detection of Objects using Electro Magnetic Wave Attenuation Patterns describe that the primary method for making an object stealthy is to reduce its radar cross section, and at one way this is achieved is that surfaces are coated with materials that absorb microwave radiation, and honeycomb sections are formed which trap microwaves, preventing reflections. Geer describes that because other countries have developed stealth technology, that it is becoming increasingly important for any military to be able to detect stealth craft. Geer proposes to detect both stealth and non-stealth craft, not by the echo of an electro-magnetic wave reflecting off an object such as in conventional radar, but rather to detect an attenuation of an electro-magnetic wave pattern due to obstruction of beam propagation by the object. Geer states that, therefore, design principles of stealth craft which seek to absorb microwave radiation will increase contrast, making them “visible”. Geer continues stating that, while beam interruption sensors are well known and used in security systems and industrially, that his system includes a number of distinctions, for example, that he does not seek to provide a narrow beam that is fully blocked by the object to be detected. Rather, Geer proposes using a beam which illuminates a much larger area than the cross section of the craft to therefore provide a region of detection significantly larger than a “line of sight” so that a large volume of space is monitored by a detector node, similar to traditional radar installations and in contrast to known shadow detectors. Geer describes his negative radar as detecting an alteration in a background radiation pattern resulting from an object interfering with transmission thereof. Geer states that the phrase negative radar refers to the effect wherein the silhouette of any craft, including a stealth craft, will block transmission of a radar beam, resulting in detectability of the attenuation of the microwave radiation.
Thus, so called stealth technology as for example applied to an aircraft, includes various aspects and different technologies working together as a system and which includes absorbing the energy of a wave propagated by conventional radar. By absorbing the incoming waves a stealth object minimizes the reflection of the incoming waves from the radar. The reflected waves which are reflected off the stealth object and sensed by the radar receiver are mis-interpreted by the radar as belonging to other than the stealth object, for example an object having a much smaller cross section. In the best case, the radar waves are not reflected at all and thus the stealth object completely avoids detection.
As would be known to one skilled in the art, other forms of stealth technology exist, such as for example so-called plasma stealth which uses a layer or cloud of ionized gas or plasma around a craft to reduce radar cross section, or other active stealth measures, or other passive stealth measures such as stealth coverings containing carbon nanotubes.